In a conventional image forming device, the following processes are performed: after the surface of a photoreceptor drum is uniformly charged by a charge roller, an electrostatic latent image is formed on the surface of the photoreceptor drum through exposing by an exposure head; a toner image is formed on the photoreceptor drum by electrostatically adhering toner that is frictionally charged and that is thinned on a developing roller; then, the toner image is transferred onto a sheet by a transferring roller; a print patter is formed on the sheet through fusing the transferred toner image; and remaining toner on the photoreceptor drum is removed by a cleaning device after the transfer.
When a number of counts of printing sheets or a number of rotations of a photoreceptor drum exceeds a predetermined reference value at the time of finishing one sheet printing, toner that stays inside of an image forming unit for a long period of time is mandatorily consumed by printing a print pattern that is expanded in the maximum width in the main scanning direction on a sheet. As a result, degradation of print quality is prevented. See Japanese laid-open patent application publication number 2003-162102 (paragraphs [0013]-[0017], [0027]-[0029], and [0034]-[0040], and FIGS. 2 and 4).
However, in the conventional technology discussed above, because toner is discarded by printing a print pattern that is expanded in the maximum width in the main scanning direction on a sheet at every time of a certain number of counts of printing sheets or a certain number of rotations of the photoreceptor drum, a certain amount of toner is constantly discarded. Therefore, there are the following problems: depending on a print pattern that is printed during intervals between certain numbers of counts of printing sheets, a waste of toner occurs because a toner discarding amount is too much; and a blot occurs because a toner discarding amount is too little.
Furthermore, because toner discarding is performed by printing toner onto a sheet, a waste of sheets occurs. When a print job for a large number of counts of printing sheets is performed, a printing for discarding toner during printing is performed. As a result, there is the following problem: operating rates of an image forming device are decreased because it takes a long period of time for print processing.
An object of the present invention is to prevent a waste of toner at the time of toner discarding and to prevent a blot from occurring by toner discarding processing that corresponds to a print pattern.